Sorry, no lists
But in most cases roller bearings are stamped with a number on the small side of on of the rings. Maybe you can read this
Or just measure the inner and outer diameter and the width of the bearing.

main bearings are the crankshaft bearings?
You are right, it's very unusuall that those are sealed.
Usually unsealed bearings with C3 or C4 gap are used. But that is not a help for you i think

<edit> I have just checked back some of my Gilera papers.
Flywheel side is C5
Clutch side is C4
Together with the measurements of the old bearings you should get something new
The parts lists only tell 'bearing'

What type of engine did you have? The one with the inlet in to the cylinder i think. APTS?
Maybe somebody with a engine similar to yours can give you a help. I think even in the parts lists are no bearing numbers or measurements to find. I fear you only can get a Gilera part number.

You only have to say this at the shop and you will get the right ones
It means that the bearings have a bigger radial play.
That is needed because the bearings are running at higher temperatures.
Don't mix them up while mounting.
I can check back the numbers at the weekend. At home i have a spare set of crank bearings.